#include <bits/stdc++.h>

using namespace std;

ifstream f("fact.in");
ofstream g("fact.out");

long long P;
long long st, dr, mid;

long long zero (long long x)
{
    long long putere=5;
    int cnt=0;

    while(putere<=x) {
        cnt+=x/putere;

        putere*=5;
    }

    return cnt;
}

int main()
{
    f>>P;
    st=1;
    dr=5*P;

    mid=1;

    while(st<=dr) {
        mid=st+(dr-st)/2;

        if(zero(mid)>=P)
            dr=mid-1;
        else st=mid+1;
    }

    g<<mid<<'\n';

    return 0;
}